Corrugated paperboard is a material used for many different shipping containers, wrap cartons and, more recently, for display shippers. In addition to shipping protection these containers need to satisfy many further requirements. One of these is that the containers must permit simple, reliable, safe and easy opening. For this purpose conventional corrugated paperboard features perforations or slits along the tear line. In part, these perforations are backed by an underbonded tear thread of tear-resistant material to render tearing open more reliable.
Known from DE 197 05 533 is an assembly for configuring a tear line for solid and compacted paperboard scored on both sides staggered by a few millimeters. When torn open, the paperboard tears in the medium plane between the troughs of the score lines. This method cannot be translated for use on corrugated paperboard since no homogenous material is involved.
GB 777,079 discloses a single-wall corrugated paperboard with tear lines, proposing as an alternative full-length incisions made only in the liners (i.e. without severing the liners completely) or a discontinuous perforation which fully perforates the liners, however. In any case, the tear lines on both sides are spaced away from each other resulting in an unsightly tear edge when torn open.
DE 693 00 351 T2 discloses a tear means for corrugated paperboard comprising a tear band and weakening lines on both sides of the tear band facing further weakening lines provided on the backing face medium. Such a system has some serious drawbacks. Thus, the system is unduly complicated not permitting round or curved tear lines to be implemented due to the plastics tear band being bonded to the carton blank. Apart from this, the freedom in designing the arrangement of the tear line is seriously restricted because of its straight-line requirement.
Known tear-open systems fail to satisfy the requirements for a container which is simple to open with no restrictions as to its structural integrity. The reason for this is that need to weaken the material of the corrugated paperboard to facilitate opening runs counter technically to the need to maintain structural integrity as required for protection in shipping. All known systems attempt to find a go-between to these contradicting requirements.
This is reflected, for example, by the German publication relating to solid and corrugated paperboard shipping cases or containers published by the European Institute of Trade (EHI) where it reads on page 13 that all of these conventional systems are unsatisfactory (unsuitable). On page 30 of this publication dating back to the year 1998 it reads that cartons having perforations are time-consuming in being opened and prompt personnel to risk making use of knives, often with serious damage to the packaged articles.